The present invention relates to semiconductor fabrication and in particular to a method of electroplating to improve gap filling performance thereof.
Copper has become a metal of choice for filling submicron, high aspect ratio interconnect features on substrates as circuit densities increase for next generation ultra large scale integration, because copper and its alloys have lower resistivity and significantly higher electromigration resistance than aluminum. These characteristics are important to enable higher current densities at high levels of integration and increased device speed.
Choices of fabrication methods for deposition of copper into very high aspect ratio features are limited because common chemical vapor deposition processes and physical vapor deposition processes have provided unsatisfactory results. Furthermore, these processes can be costly. As a result, electroplating or electrochemical plating is becoming an accepted method of copper metallization of interconnect features on semiconductor devices. However, undesirable gap filling sometimes occurs in metal electroplating and causes poor device performance due to issues such as unoptimized tool design or chemical breakdown of the electrolyte during metal electroplating.
In U.S. Pat. No. 6,399,479, Chen et. al. disclose a process to improve electroplating fill of metal. In the U.S. Pat. No. 6,399,479 patent, a portion of the seed layer formed on sidewall portion of a semiconductor structure is removed using a electrochemical de-plating process prior to the electroplating process of the metal.
Nevertheless, conventional metal electroplating such as copper plating is performed by an electroplating apparatus under a temperature near the cleanroom temperature, and the electroplating temperature is controlled by directly adjusting the temperature of an electrolyte storage tank for supplying the electrolyte to the electroplating apparatus.
During the Cu electroplating, film qualities such as film thickness distribution or gap filling capability can be affected by the temperature of the electrolyte. Direct adjustment to the temperature of the electrolyte storage tank may seriously degrade additives such as suppressors, accelerators and levelers added therein and chemical breakdown thereof occurs in the electroplating apparatus, thus resulting in poor thickness distribution, and poor gap filling of the electroplated film or forming an electroplated film having undesirable particles thereon.
Hence, there is a need for a better electroplating method to address the potential issues such as chemical breakdown in the electrolyte, to improve the film quality of the electroplated metal film.